Significant contributions of biomass burning to PM2.5-bound aromatic compounds: insights from field observations and quantum chemical calculations

Abstract

Polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs (OPAHs), and nitrophenols (NPs) are essential aromatic compounds that significantly affect both climate and human health. However, their sources and formation mechanisms, particularly for NPs, remain poorly understood. This study determined the concentration profiles and the main formation mechanisms of these substance classes in PM2.5 from Dongying, based on field observations and quantum chemical calculations. The daily concentrations of ĝ'13PAHs during heating were more than twice higher compared to those before the heating period. Benzo(b)fluoranthene was identified as the primary PAHs species. The average concentration of ĝ'8OPAHs reached 351 ng m-3, with significantly increased concentrations observed during the heating season (15 November-6 December 2021) wherein 1-Naphthaldehyde (1-NapA) emerged as the most prevalent OPAH species. Concentrations of ĝ'9NPs increased approximately 1.2 times during the heating, with 4-methyl-5-nitrocatechol (4M5NC) having the highest concentration. Positive matrix factorization (PMF) analysis identified biomass burning to be the primary source of these aromatic compounds, particularly for PAHs. Density functional theory (DFT) calculations further revealed that phenol and nitrobenzene are two main primary precursors for 4-nitrophenol, with phenol showing lower reaction barriers, and P-Cresol was identified as the primary precursor for the formation of 4M5NC. This study provides the first detailed investigation of the sources and formation mechanisms of aromatic compounds in the atmosphere of petrochemical cities, using Dongying in the Yellow River Delta as a representative case study. This investigation may provide fundamental insights and important guidance for reducing emissions of aromatic compounds in similar atmospheric environments.